Pressure responsive switch



April 21, 1964 v. M. JEMISON PRESSURE RESPONSIVE SWITCH 2 Sheets-Sheet 1Filed Nov. 8, 1960 w w w w W W April 21, 1964 v. M. JEMISON PRESSURERESPONSIVE SWITCH 2 Sheets-Sheet 2 Filed Nov. 8, 1960 INVENTOR. VOLNEYM. azwsou ATTO EY 'which the switch is responsive, and

United States Patent 3,130,281 PRESSURE RESPONSIVE SWITCH Voiney M.Jamison, Phoenix, Aria, assignor to Thunderlrird Engineering C0,,Phoenix, Ariz., a corporation of Arizona Filed Nov. 8, 1969, Ser. No.68,074 7 Claims. (Cl. 200-83) The present invention relates to pressureresponsive switches. It relates more in particular to a switch whichoperates in response to static pressure within a liquid hydraulic systemfor controlling some aspect of such system.

Many types of pressure responsive switches have been produced in thepast, but all leave something to be desired either from the standpointof cost, useful life or reliability. Commonly such switches haveemployed a diaphragm to seal off the switch housing against entrance ofthe hydraulic fluid, such as water, being controlled. Simpleconstructions associated with the use of a diaphragm are frequentlysubject to leakage, and commonly the leakage is not detected insuflicient time to prevent complete failure. Still another problem withmany such switches is an inability to control precisely the pressurewithin the hydraulic fluid to which the switch is responsive; and ininstances where precise control has been possible, costs generally havebeen sufficiently high to limit applicability of such switches torelatively expensive type installations. Heretofore none of the switchescommonly available on the market combined the advantages of low cost,precision control and reliability to such extent that such switchescould be used to advantage in systems normally employed in thehousehold.

Accordingly, the principal object of the invention is the provision ofan improved pressure responsive switch which combines the features ofrelatively low cost, such precision operation as may be required andlong reliable useful life.

Another object of the invention is the provision of an improved pressureresponsive switch adaptedfor use in pressure systems containing aqueousliquids.

Still another object is the provision of improved means forpredetermining and controlling the pressure to which the switch isresponsive.

Other specific objects and features of the invention will be madeapparent from the following detailed description taken with theaccompanying drawings, where- FIG. 1 is a perspective view showing oneform of the present invention, the figure being to a scale approximatelytwice actual size; I

FIG. 2 is a central longitudinal sectional view taken on the line 2-2 ofFIG. 1; 7

FIG. 3 is a fragmentary sectional view taken on the line 3-3 of FIG. 1;

FIG. 4 is an enlarged perspective view showing the interior of theswitch housing as it is produced before assembly of the switch elementstherein;

a preferred contion;

FIG. 7 is a further enlarged fragmentary sectional view showing themanner in which the diaphragms'are supported and the means provided forequalizing pressures between them;

FIG. 8 is an enlarged transverse sectional view showing a simplifiedform of the invention in which only one pair of contacts is employed;

FIGS. 9 and 10 are views of the housing assembly only of a switchwith asingle pair of contacts as in FIG. 8, but showing improved means forsetting the pressure to to prevent link 36 from rotating around itsterminal rivet 3,130,281 Patented Apr. 21, 1964 invention shown in FIGS.1 through 7 there are three contacts and three terminals so that thesame switch may operate on a normally. closed circuit basis or on anormally open circuit basis. This embodiment also shows the use of acoil compression spring for controlling the loading of the switch arm topermit control of the pressure to which the switch is responsive over arelatively wide range. In most actual installations the switch isfurnished to be used on either a normally closed circuit or normallyopen circuit; and it is also frequently furnished pre-set for responseto a given pressure. Any such variations in the switch itself are madeentirely in the housing assembly,remaining portions of the switchv atall times being identical. The features which permit this selection ofelements and simplification of the switch for particular typeinstallations will appear as the description progresses.

Referring further to the drawings, the housing assembly includes agenerally cup shaped housing 17 (FIG. 4) made of suitable non-conductingmaterial such as phenolic resin of the type known in the trade asBakelite. It has an annular bottom terminal'fiange 18 which cooperateswith the body 10 as will be described to effect the final assembly. Arivet type terminal 19 has a press fit through a hole in the housing andthrough an edge projection 21 integral with the housing where it isriveted over to support a switch arm 22 formed of suitable conductivespring material such as beryllium copper or Phosphor bronze. As shownparticularly. in FIG. 4, the edge projection 21 has a shallowrecesswhere the switch arm 22 attaches to positively position such arm andprevent its rotation around the rivet contact 19. The switch arm 22carries a contact point 23 at its free end. Suitably, also, the centerportion of the contact arm 22 is. convoluted to impart improved springaction and also to provide a seat for a phenolic plunger 24 springpressed downwardly by a coil spring 26, the compression of which may becontrolled by a set screw 27. Preferably the plunger 24 is formed of aphenolic plastic and the screw 27 of nylon plastic, although anysuitable non-conducting materials may be used.

A link 28 secured in position by a terminal rivet 29 (FIG. 3) lies alongthe inner top surface of the housing 17. The link 28 is formed ofsuitable conductive material such as Phosphor bronze and carries acontact 31 in alignment with the contact 23 on the switch arm 22. An

anchoring tab or projection 30 integral with the link 28 lies along theinside surface of the housing 17 and thus 34 from the housing and isriveted to anchor a switch link 36 having a contact point 37 inalignment with the contact point 23 on the switch arm 22. The link 36also has a tab 35 bent at right angles tothe plane of the linkitself'and engages along the side edge of projection 34 32. The links 28and 36 are thus identical, except that one has its anchoring tab in theplane of the link and one has it turned at right angles. Because of theposition of the projection 34, the link 36 is spaced vertically from thelink 31 so that the link contacts are on opposite sides of the armcontact. Normally the contact points 23 and 37 are in engagement. Theterminal 32, link 36 and contact point 37 are therefore effective whenthe switch is used in a normally closed circuit.

The body It) is preferably turned from a solid piece of corrosionresistant metal such as brass and has a cup shaped portion 41 and aninteriorly and exteriorly threaded shank 42 for attachment of the switchto a pipe, tank or the like for functional communication with the fluidto which it is responsive through an opening 43 extending through theshank 42 into the cup shaped portion 41. The base of the cup shapedportion is provided with an annular slot 44 with an annular shallow area45 inside the slot 44 and an annular raised portion 46 outside the slot44 (FIG. 7), the function of which will be referred to hereinbelow. Theactuating piston has a relatively wide head 47 against which hydraulicpressure is effective and a relatively smaller diameter switch armengaging portion 48 connected by a tapered side portion 49 which engagesa matching tapered side portion 51 on the spacer 13. The spacer 13 asshown in FIG. 6 has an annular opening 52 (FIG. 6) for the passage ofthe switch arm engaging portion 43 of the actuating piston and also anexterior annular ring 53 raised from its top flat face, the function ofwhich will also be referred to hereinbelow. It should be noted also thatthe piston is thicker than the spacer, so that when the piston has beenraised by action of hydraulic pressure and the tapered surfaces 49 and51 are in firm engagement the switch arm engaging portion 48 of thepiston will project upwardly above the spacer and lift the switch arm22.

The parts as shown in FIG. 6 are assembled and sup, ported in a suitabledie, the upper edge of the body being crimped over the top of theannular projection 18 of the housing 17 as at 54 in FIG. 2 to completethe assembly. Normally a total pressure of about two tons in an arborpress with a suitable crimping die is effective to produce an assemblyin which the diaphragms 14 and 11 are so firmly clamped together as tominimize the possibility of leakage. A hole 56 (FIG. 1) is provided inthe cup shaped portion 41 of the body between the two diaphragms. Thisnot only minimizes the possibility of fluid reaching the switch housingif a leak should develop around the diaphragm 11, but it also stabilizesthe pressure between the diaphragms and serves as a warning that theswitch should be replaced in case leakage should appear.

Pressure responsive switches using a pressure respon sive switchoperating member such as a diaphragm and sealing means for preventingthe hydraulic fluid from fouling the switch elements have in the pastpresented several problems. Free movement of the actuating memher andeffective seal thereof are important, and in general diaphragm membershave served Well for such purposes. In relatively small switches usingsimple diaphragms, clamping action adequate to seal the diaphragm edgesfrequently injure them and reduce their effective life. Development ofdifferential pressures also have the effect of making such switchessluggish or inoperative. Such pressures may develop from hydraulicleakage, from release of gases occluded from parts and from othercauses.

To seal the diaphragm 11 effectively, it is squeezed between the fiatbottom face of the spacer 13 and the annular surface 45, its edge beingcrimped on the edge defined by the annular slot 44 and partially foroeddown into such slot. The outside edge of the spacer 13 rides on theraised annular surface 46, so that the space between the spacer 13 andannular surface 45 is just sulficient to grip the diaphragm 11 tightlybut is not shallow i enough to crush the diaphragm. Similarly, diaphragm14, the effective sealing is somewhat less important, is squeezedbetween the bottom edge of flange 18 and the top of spacer 13. The ring53 holds the flange 13 and spacer slightly apart so that the diaphragm14 is gripped tightly but not crushed.

As shown particularly in FIG. 7, the side edge of the spacer 13 isslightly tapered to provide a slight circular space 57 between thespacer and the interior annular surface of the cup shaped portion 41 ofthe body 10. A radially positioned hole 58 in the spacer 13 places thiscircular space 57 in communication with the center opening 52 of thespacer, and then in communication with the entire space between the twodiaphragms. Since the hole 56 in the cup shaped portion is incommunication with the circular space 57, the entire space between thetwo diaphragms is substantially at ambient pressure. Thus the hole 56not only acts as a bleed hole if hydraulic fluid should seep bydiaphragm 11, but, with the remaining structure described has animportant pressure equalizing function. The action of the diaphragms andthe action of the piston 12 thereby remain substantially uniform duringthe useful life of the switch.

While the various parts of the switch may be constructed of differentmaterials within the limits of the required specifications regardingconductivity and dielectric strength, phenolic plastic is preferred forboth the actuating piston 12 and the spacer 13. Very good results havebeen obtained using diaphragms of nylon cloth impregnated with buna-Nrubber. The contact points are preferably of silver. While the switchhousing does not require a pressure seal, it is preferred that it besealed climatically and to this end the terminals 19, 29 and 33 arepreferably made slightly tapered so that when they have a press fit intopreviously prepared holes drilled in the housing 17 riveting all theirends over to secure in place with the switch arm 22 or one of the links28 or 36 will effectively seal the holes through the housing. The switcharm 22 and links 28 and 36 may be given a slight plating of gold orotherwise treated to reduce the amount of occluded gases entering thehousing in which they are sealed. By carefully dimensioning the nylonspring adjusting screw 27 and using a suitable thread sealout, aclimatic seal may also be obtained at this point. The bottom of thehousing, of course, is sealed by the diaphragm 14.

The switch shown in FIGS. 1 through 6 has three terminals but is notcommonly used with more than two such terminals. The specific switchelements used are selected depending on whether the switch is intendedfor use on a normally open or normally closed circuit. Switches of thetype disclosed herein are normally utilized in relatively largequantities for a given use. If that use is to be with a normally closedcircuit, for example, there is no reason why the added cost of providingthe second terminal and set of contacts should be incurred. The housing17 is molded without any holes in its top surface; and to provide onlytwo contacts, all that is necessary is to drill out only two terminalreceiving holes and install only the switch arm 22 and the required link28 or 36.

The pressure to which the switch is responsive may be controlled in partby the switch arm 22 and in part by the spring 26. By leaving out thespring assembly entirely and varying only the thickness of the metal ofthe switch arm, a variation in pressure to which the switch is respons iv e of between one to six pounds or more pressure is easily possible.When using the spring 26, a variation in pressure from one to onehundred pounds is easily possi ble, and operation at fifty to sixtypounds pressure is easily possible without markedly shortening theuseful life of the switch. Since the pressure to which the switch is tobe responsive in a given system is usually known and always uniform, formany purposes the entire spring assembly may be left out as shown inFIG. 8, in which case only the switch arm is effective. Under suchcircumstances with a known relatively low spring loading required for aparticular installation, the housing 17 is not drilled at its center andnone of the parts comprising the spring assembly is included in thecompleted switch. The thickness of the switch arm 22 will then determinethe pressure at which the switch operates. It has been found that with apreset pressure within the range obtainable by a single spring contactarm, the variation from switch to switch may be controlled well withinthe operating limits of systems in which the switch is used.

In the switch shown in FIG. 8, I have employed the same referencecharacters as those shown in the previously described figures, becauseit is not in effect a modification, but the same switch using only thelink 28 and a related parts, including the switch arm 22 pre-set to thedesired pressure response and without the spring assembly. The switchshown in FIG. 8 is assembled for use in a normally open circuit.

While utilizing the features of the present invention heretoforedescribed the generally conventional spring pressed follower shown inFIG. 2 may be utilized successfully to control the pressure to which theswitch is responsive, I have found that this construction isrelativelycostly and at times subject to difficultly controllable variables makingeffective setting difiicult andcostly. These problems are accentuatedwhen the switch is made in relatively small sizes having, for example,an overall diameter of the order of an inch or less, and an overallvertical dimension of approximately 1% inches. A switch of thisrelatively small size is extremely desirable and effective for manytypes of installations. In FIGS. 9 through 11 I illustrate a relativelysimple, novel and extremely effective construction by means of whichvery accurate control of the pressure to which the switch is responsivemay be obtained, and such pressure readily and inexpensively pre-set inthe switch during the course of its assembly. This is to be contrastedwith a situation in which itmay be necessary to re-check the adjustmentof the switch after it has been installed within a pressure system inaccordance with its intended use.

For convenience of illustration I have shown in FIGS. 9 and 10 only theswitch housing assembly, and have employed therein the same referencecharacters used in the preceding embodiments to identify identicalparts. The switch there shown is adapted for use on a normally opencircuit, the contacts being closed in response to pressure within thesystem with which the switch is employed. In FIG. 9 the switch is set tobe responsive at zero pressure, that is to say, the contacts 31 and 23associated with the link 28 and the switch arm 22 respectively beingclosed. In FIG. 9 the contacts are open, the switch being set forexample for 2 to 10 pounds operation depending on the requirements ofthe system.

In FIG. 11 I SilDW the details of the switch arm 22 and a pressure plate61 which is adapted to be engaged by a nylon screw 62 threaded throughthe top face of the housing 17 and through the flat projection 21 towhich the switch arm 22 is connected by the rivet-type terminal 19. Thefollower 6. has a fiat attaching area 63 which sets under the flatportion of the switch arm 22 and is secured in place with the switch armby the rivet-type contact 19. It also has an offset defining a shoulder64 and a screw engaging portion 66.

As FIG. 9 clearly shows, the shoulder 64 lies immediately above thearcuate center portion of the switch arm 22 but is out of contacttherewith when the screw 62 is adjusted to an upper position. Underthese conditions the switch arm 22 through its center curved portion isbiased upwardly in the direction of the contact 31 so that the contact31 is actually engaged by the contact 23. This positioning isillustrative, obviously, as the switch arm may readily be shaped so thatin its normal position it will clear the stationary contact and willrequire a pressure of say one-half pound, one pound or similar desiredvalue which would represent the minimum possible setting to which theswitch could be adjusted. When the screw 62 is turned downwardly,however, using for example a small screw driver or other suitable tool,the shoulder 64 rides against one edge of the curved portion of theswitch arm nearest the flat mounting portion of the switch arm; Thepressure plate 61 may, for example, havelhosphor bronze, berylliumcopper or other such spring material (it'does not have to have lowconductivity because it does not carry any of the current) so that itsoverhanging portion may readily be deflected downwardly with theshoulder 64 in contact with the switch, and it willretain whateversetting it is given and will always return to the initial position fromwhich it was originally deflected. Notwithstanding the smallness of theparts, precise controlof the pressure required to return the switch armto contact closing position can be obtained simply and inexpensivelywithin limits of up to 15 pounds or more using the identical designshown.

It should be understood that any of the features illustrated in theseveral embodiments except thosemutually replacing each other maybecombined in producing a switch having the requirements to meet aparticular specification. A switch utilizing the pressure plateadjustment shown in FIGS. 9 through 11, for example, may be replacedwith a switch operated in a normally closed circuit or in a switchemploying two sets of contacts such as shown in FIG. 2.

One of the principal advantages of the present invention, in addition toits relative simplicity, versatility and relatively low cost, is itsfreedonifrom defects such as would shorten its useful life. A switchidentical to that shown in FIG. 8 for example was operated for over10,000,000 cycles and continued to function without failure.

Various modifications of the invention may be made within the scope ofthe appended claims.

I claim: I

1. A pressure responsive switch comprising a switch housing assemblyincluding a housing member with a bottom annular flange and electricalswitch means in the housing, a body member adapted for attachment to ain, a switch actuating piston on the side of the spacer facing the bodywith a switch operating head projecting through the spacer opening,means between the actuating piston and spacer for limiting movement ofthe said actuating piston in the direction of the switch assembly, andmeans clamping together said body and the switch housing assembly toclamp the said diaphragms between the cup shaped bottom portion andspacer, and between the spacer and switch housing respectively.

2. A pressure responsive switch as defined in claim 1 wherein saidbottom of the cup shaped member and one face of the spacer are providedwith annular diaphragm engaging portions and spacing portions whereby toprovide adequate pressure to clamp the diaphragms but not to crush them.

3. A pressure responsive switch comprising a switch housing assemblyincluding a housing member with a bottom annular flange and electricalswitch means in the housing, a body member adapted for attachment to ade vice containing flluid under pressure, said body member including acup shaped portion with bottom and annular side wall, a spacer betweensaid bottom and switch housing assembly, imperforate diaphragms onopposite sides of the spacer, said spacer having a central openingtherein, a switchactuating piston on the side of the spacer facing thebody with a switch operating head projecting through the spacer opening,means between the actuating piston and spacer for limiting movement ofthe said actuating piston in the direction of the switch assembly, and

means clamping together said body and the switch housing assembly toclamp the said diaphragms between the cup shaped bottom portion andspacer, and between the spacer and switch housing respectively, saidbottom of the cup shaped member and one face of the spacer beingprovided with annular diaphragm engaging portions and spacing portionswhereby to provide adequate pressure to clamp the diaphragms but not tocrush them and wherein a bleed hole is provided in the side wall of thecup shaped member between the said diaphragms, whereby to place thespace between the diaphragms in communication with ambientatmosphericpressure.

4. A pressure responsive switch as defined in claim 1 wherein said bodyhas an annular slot facing the spacer with an annular interior recessedportion on one side of the slot and an annular exterior raised portionon the other side of the slot, the facing side of the spacer being fiat,whereby said spacer engages said raised portion and the diaphragm isclamped against the recessed portion and edge between same and saidannular slot, said spacer having an exterior upper ridge engaging thehousing to thereby leave a space between the facing surfaces of thespacer and housing within which the second diaphragm is clamped, wherebythe maximum clamping pressure applied to the diaphragms is controlled tothereby firmly clamp did not crush such diaphragms.

5. A pressure responsive switch comprising a switch housing assemblyincluding a housing member with a bottom annular flange and electricalswitch means in the housing, a body member adapted for attachment to adevice containing fluid under pressure, said body member including a cupshaped portion with bottom and annular side wall, a spacer between saidbottom and switch housing assembly, imperforate diaphragms on oppositesides of the spacer, said spacer having a central opening therein, aswitch actuating piston on the side of the spacer facing the body with aswitch operating head projecting through the spacer opening, and meansbetween the actuating piston and spacer for limiting movement of thesaid actuating piston in the direction of the switch assembly, saidannular side wall of the cup shaped body portion being crimped aroundthe annular flange of the switch housing assembly to clamp the saiddiaphragms between the cup shaped bottom portion and spacer, and betweenthe spacer and switch housing respectively.

6. A pressure responsive switch comprising a switch housing assemblyincluding a housing member with a bottom annular flange and electricalswitch means in the housing, a body member adapted for attachment to adevice containing fluid under pressure, said body member including a cupshaped portion with bottom and annular side wall, said cup shapedportion being crimped around said flange to hold the switch housing andbody member together, a spacer between said bottom and switch housingassembly, imperforate diaphragms on opposite sides of the spacer, saidspacer having a central opening therein, a switch actuating piston onthe side of the spacer facing the body with a switch operating headprojecting through the spacer opening, and means placing the entirespace between the diaphragm in communication with ambient atmosphere.

7. A pressure responsive switch comprising a switch housing assemblyincluding a housing member with a bottom annular flange and electricalswitch means in the housing, and means projecting through the housingfor adjusting the pressure at which the switch means responds, a bodymember adapted for attachment to a device containing fluid underpressure, said body member including a cup shaped portion with bottomand annular side wall, a spacer between said bottom and switch housingassembly, imperforate diaphragms on opposite sides of the spacer, saidspacer having a central opening therein, a switch actuating piston onthe side of the spacer facing the body with a switch operating headprojecting through the spacer opening, and means between the actuatingpiston and spacer for limiting movement of the said actuating piston inthe direction of the switch assembly, said annular side wall of the cupshaped body portion being crimped around the annular flange of theswitch housing assembly to clamp the said diaphragms between the cupshaped bottom portion and spacer, and between the spacer and switchhousing respectively.

References Cited in the file of this patent UNITED STATES PATENTS1,231,561 Briggs July 3, 1917 2,275,556 Rasmussen Mar. 10, 19422,317,271 Higley et al. Apr. 20, 1943 2,741,675 Chase et al. Apr. 10,1956 FOREIGN PATENTS 620,958 Great Britain Apr. 1, 1949

1. A PRESSURE RESPONSIVE SWITCH COMPRISING A SWITCH HOUSING ASSEMBLYINCLUDING A HOUSING MEMBER WITH A BOTTOM ANNULAR FLANGE AND ELECTRICALSWITCH MEANS IN THE HOUSING, A BODY MEMBER ADAPTED FOR ATTACHMENT TO ADEVICE CONTAINING FLUID UNDER PRESSURE, SAID BODY MEMBER INCLUDING A CUPSHAPED PORTION WITH BOTTOM AND ANNULAR SIDE WALL, A SPACER BETWEEN SAIDBOTTOM AND SWITCH HOUSING ASSEMBLY, IMPERFORATE DIAPHRAGMS ON OPPOSITESIDES OF THE SPACER, SAID SPACER HAVING A CENTRAL OPENING THEREIN, ASWITCH ACTUATING PISTON O NTHE SIDE OF THE SPACER FACING THE BODY WITH ASWITCH OPERATING HEAD PROJECTING THROUGH THE SPACER OPENING, MEANSBETWEEN THE ACTUATING PISTON AND SPACER FOR LIMITING MOVEMENT OF THESAID ACTUATING PISTON IN THE DIRECTION OF THE SWITCH ASSEMBLY, AND MEANSCLAMPING TOGETHER SAID BODY AND THE SWITCH HOUSING ASSEMBLY TO CLAMP THESAID DIAPHRAGMS BETWEEN THE CUP SHAPED BOTTOM PORTION AND SPACER, ANDBETWEEN THE SPACER AND SWITCH HOUSING RESPECTIVELY.